Cleveland is one of the Aleutian Islands’ most active volcanoes. It’s been on watch for the better part of the past two years, and in June it blew ash 35,000 feet high.

Today’s explosion was small by comparison and didn’t produce a visible ash cloud, according to the Alaska Volcano Observatory. Since there isn’t any real-time monitoring equipment on Cleveland, the explosion was detected using infrasound and seismic equipment on nearby volcanoes.

Cleveland lies on uninhabited Chuginadak Island, about 115 miles away from Unalaska and 900 miles from Anchorage. While there isn't a population center near the volcano, it does lie below a major international flight path and could cause major air traffic problems in the event of a serious eruption.